Micromechanical mirror structures (in short, micromirrors) are known, which are made, at least in part, of semiconductor materials and using MEMS (Micro-Electro-Mechanical Systems) technology.
These micromechanical structures may be integrated in electronic devices, in particular portable or mobile devices, such as, for example, portable computers, laptops, notebooks (including ultra-thin notebooks), PDAs, tablets, phablets, smartphones or wearable devices, for optical operations, for example for directing in desired scanning patterns light radiation beams generated by a light source, e.g. a Laser.
Thanks to the reduced dimensions, these structures enable stringent requirements to be met as regards occupation of space, in terms of area and thickness.
For example, micromirrors are used in miniaturized projector modules (so called “picoprojectors”), which are able to project images at a distance or to generate desired patterns of light, in the visible or infrared spectrum; in barcode scanners; or in laser printers.
Micromirrors generally include: a mirror element, obtained from a body of semiconductor material in such a way as to be movable, for example with a tilting or rotation movement, to direct a incident light beam according to a desired scanning pattern; and a supporting structure, which is also obtained from a body of semiconductor material, is coupled to the mirror element, and has supporting and handling functions. A cavity is made in the supporting structure, underneath, and in a position corresponding to, the mirror element, in such a way as to enable freedom of movement for tilting or rotation thereof.
During operation, application of an AC voltage with a proper frequency causes oscillatory movement at the mechanical resonant frequency of the micromechanical structure. Actuation at the resonant frequency allows high frequency operation, thus allowing to achieve a high scanning speed.
The Applicant has realized that the above discussed driving structure, although advantageous, may not be optimized, at least for some operating conditions.
In particular, due to the sinusoidal pattern of the micromirror movement, it is required to compensate the variation of the scanning speed, when there is a need of projecting light at a uniform intensity level (to achieve a substantially uniform brightness).
Indeed, the sinusoidal micromirror movement is faster at the center of the movement pattern and slower at the edges, so that a suitable modulation of the power and intensity of the light to be projected is required. Accordingly, the power and/or frequency rate of the light source has to be modulated by a suitable control logic to match the speed variation of the micromirror during its scanning pattern.
In particular, this modulation entails lowering of the power of the light source at the edges of the scanning pattern, when the micromirror speed is slower, resulting in a decrease of the total power that is produced at the output.
Indeed, it is possible to show that the light power is about 63%, if compared to the case in which the light source were kept at full power along the entire scanning pattern; the light brightness available at output is thus reduced by about 37%.
Micromirrors of a linear type do exist; however, they are complex to manufacture, entail lower scanning aperture and lower operating speed and generally more complex driving structure.
There is a need in the art to overcome, at least in part, the issues highlighted previously.